Due to the proliferation of personal computers, the widespread acceptance of the Internet, and the advent of the Information Age, there is a virtual explosion in the amount of digital data transmissions. Currently, one common method for transmitting and receiving digital data involves the use of telephone modems. A telephone modem is used to transmit digital data generated by a computer to an intended destination over standard telephone lines. The same modem also can receive digital data from a telephone line. This setup enables computers to gain access to the Internet and other on-line services over standard telephone jacks. Although this form of communications is convenient, it is painfully slow because telephone lines simply consist of pairs of twisted copper wires. These lines were primarily designed to carry analog voice signals rather than digital data. As such, telephone lines are bandwidth limited, and the rate at which digital data can be transmitted is relatively quite slow. It can take several minutes or even hours to download picture, audio, and video files via standard telephone modems. Hence, telephone modems are not ideally suited for conveying video (e.g., teleconferencing, movies, etc.), graphics (e.g., computer-aided design, medical imaging, simulations), or multimedia applications.
A faster medium for high-speed communications entails the use of dedicated computer networks, whereby computers are interconnected to form local area networks or wide area networks (LAN/WAN). However, the downside to this approach is the high cost of purchasing, routing, and maintaining the requisite interconnecting coaxial and hybrid fiber lines. Furthermore, highly skilled network administrators are necessary to monitor the network in order to keep it operational. In addition, expensive networking equipment (e.g., routers, hubs, repeaters, concentrators, servers, bridges, etc.) must be purchased and installed. Hence, the advantage of having faster data communications and higher bandwidth comes at a steep price. Furthermore, it is prohibitively expensive to set up dedicated computer networks amongst individual homes.
There is, however, another medium which is already in place and is widespread and which also has a very high bandwidth suitable for transmitting vast amounts of information. This medium is the cable TV (CATV) systems. CATV is comprised of coaxial and fiber optic cables which have very high transmission capacity. In the past, CATV was primarily limited to being a one-way only transmission medium, whereby TV signals were distributed from a central "head-end" terminal, over the CATV network, to a number of subscribers' television sets. But instead of simply broadcasting TV signals, it is feasible to use these CATV networks to provide high capacity two-way data communications. By implementing subscriber terminal units (STUs) or cable modems, computers can transmit and receive data packets at high data rates over existing fiber coax CATV systems. In fact, developers have been working on such systems for delivering various digital data over standard CATV systems.
Presently, STU and cable modem designs follow the same configuration as telephone modems did in the past, in that they are typically stand-alone, self-contained units. As such, STUs suffer from several deficiencies. First, it can take a relatively long time to install an STU because the STU initially has to find and acquire a channel for its transmissions. Installing a single STU can take upwards of half an hour. Consequently, upgrading an existing cable system or installing a new cable system with thousands or even millions of these STUs can be a very costly and time-consuming task. Another deficiency with having a self-contained unit is that it is extremely difficult for a single STU design to accommodate all the different standards and formats existing today. It is even more difficult to predict, anticipate, and support future standards and formats (e.g., "firewire" IEEE 1394, Universal Serial Bus, etc.). Another deficiency with self-contained designs relates to diagnostics. Some prior art STUs incorporate built-in self test circuitry within each and every unit for purposes of performing diagnostics. However, it is costly to implement this added circuitry with every unit. Other prior art designs do not include any testing circuitry within the unit. This approach requires that a malfunctioning unit be shipped back to the manufacturer, which then disassembles the unit and hooks it up to specialized test equipment in order for diagnostics to be performed. Although the cost of each unit is minimized, performing troubleshooting and diagnostics is very inconvenient and inefficient. Yet another deficiency with implementing a self-contained unit pertains to flexibility and functionality. Some subscribers may wish to use the STU solely for exchanging digital data (e.g., Internet and Web browsing, email, etc.), whereas other subscribers may desire other types of services (e.g., video on demand, home shopping, telephony, interactive gaming, etc.). Shipping STUs with the full range of functionalities is prohibitively expensive, especially if a large number of subscribers is not even interested in subscribing to and paying for these enhanced services. On the other hand, it would be attractive if a cable operator could offer these services as options and capture the revenues of interested subscribers.
In addition, present Asymmetric Digital Subscriber Line (ADSL) modems also suffer from many of the same problems as discussed above. Namely, it is difficult for diagnostics to be performed in the field for an ADSL modem. Furthermore, it is difficult or even impossible to enhance the functions or upgrade the services of current ADSL modems.
In recognition of these deficiencies, the present invention offers a solution by implementing an application interface module (AIM). Basically, the STU of the present invention contains a slot into which any one of several different AIM modules can be inserted. These AIM modules have specific circuitry for facilitating and enabling a wide variety of functions. The AIM module of the present invention can also be adapted to work with ADSL technology.